Proppant is used in hydraulic fracturing operations and added to the fracturing fluid to keep an induced hydraulic fracture open, during or following a fracturing treatment. Proppants vary in composition depending on the type of operation and/or fracturing fluid used. Recently, there have been efforts to improve flow characteristics and chemical transport of proppant.
Notwithstanding the efforts made to improve proppant, the specific gravity of most proppant ranges between about 2.20 g/cc to about 3.67 g/cc, causing proppant to rapidly settle out and/or prematurely bridge off in the hydraulic fracture. For example, certain proppant have been pumped and coated with nitrogen to produce a thin surfactant coating that causes a layer of nitrogen to attach to particles of proppant. The nitrogen temporarily reduces the apparent specific gravity of the proppant and reportedly improves proppant transport by about 25%. Another proppant has been developed with a polymer coating that expands when hydrated. The coating effectively reduces the density of the proppant while it is being pumped. The polymer then dissolves with conventional breakers once it settles in the hydraulic fracture.
There is also high-drag proppant shaped like an “X” instead a sphere. The shape is designed to interlock with other particles to reduce proppant flow back and reportedly increases drag and reduces settling rates by about 27%. Further an in-situ proppant that is polymer-based fluid forms spherical particles within the fracture. Particles in this proppant are activated by catalysts and reservoir temperature.
Even viscous gels have been used to hold the conventional proppant in suspension. However, incomplete removal or cleanup of these complex gels injected into the formation cause significant formation damage by plugging up most of the created hydraulic fracture.
Attempts to improve proppant typically suffer from high cost and/or lack of compressive strength. To compensate for the high cost, the proppant can be pumped in very low concentrations to form a single, high conductivity layer (monolayer) on top of the “proppant pack” in an effort to increase well productivity. However, this approach has rarely proven to be commercially effective. As result, the ultra-light weight proppants are rarely pumped today for stimulating subterranean formations. Moreover, because of low compressive strength, commercial applications of these proppants are typically limited to shallow, low pressure formations.
A need exists, therefore, for proppant having new and improved properties in order to more effectively stimulate subterranean formations with far less environmental impact than is possible with the conventional proppant.